If a celebrity draws attention to a global issue, it will aware many common people about this problem. Fans who are already aware, will appreciate him. Some Fans who knows nothing about climate change may not care and forget his particular speech. Few fans will think for some minutes about the subject what their hero tries to tell. These minutes of their thinking will be a gain to mankind.
The saying of Leonardo is more philosophical than based on sound scientific data. People with meagre (most Politicians) to advanced knowledge of "Climate Change" are entitled to express their views. How it is perceived by an individual is important - not spread via media to masses.
I've just thought that almost every celebrity in USA (most of them can be called world stars) promotes ecological worldview and lifestyle, but the fans don't hurry to live that way. They maybe think about it for a while, but there it ends. Considering the influence of modern american culture, most people in the world should be ecological activists by now.